The present invention relates to a method for separating sludge-like material and water, said sludge-like material hang a specific mass that approaches the specific mass of water, in which method a suspension, comprising water and sludge, is moved through a container.
A method of this type is generally known in the prior art. The aim is to cause the sludge-like material to float to the top with the aid of flotation techniques and the material that is forced up is skimmed off with the aid of skimming equipment. Separate foaming agents and the like are needed for this purpose. The addition of said agents not only incurs costs, but frequently gives rise to farther contamination of the water,
Other methods for separating sludge-like material and water comprise heating, as a result of which water is removed by evaporation and sludge-like material remains behind. A method of this type is particularly energy-intensive and has been proposed, for example, for concentrating manure-like materials.
From the Japanese patent application 57094388 a method is known to suppress and prevent the floating and concentrating of sludge. Removal of anaerobic gas is realised by subjecting sludge to flow of air. After aeration sludge is bent to a separate container for further processing.
The aim of the present invention is to provide a method with which water and sludge-like material are essentially separated from one another without further chemicals or highly energy-intensive steps being required for this purpose.
This aim is achieved with a method as described in that a vertically ascending steam of finely divided air bubbles is fed through the sludge suspension in the container and in that a stream containing sludge-enriched fluid is drained from the lower section of the container.
The insight on which the invention is based is, in contrast to the prior art, not to make use of flotation for the sludge-like material but to lower the apparent specific mass of water by feeding in air, as a result of which settling of sludge takes place because the specific mass of the sludge is then higher. The sludge can then be discharged.
The method described above can be used, inter alia, for concentrating manure-like materials.
However, surprisingly it has been found that the method can also be used for cleaning products such as (flower) bulbs. Soil material always adheres to bulbs of this type and for export to certain countries the regulations lay down that there must be absolutely no soil material adhering to such bulbs. For this purpose, in the prior art, the bulbs are subjected to a spray-treatment with water under high pressure. Damage to the bulbs regularly occurs as a result and there is no guarantee that grains of sand and the like have also been completely removed from the bulbs.
Another method for cleaning bulbs is to introduce them into drums of large diameter, for example having a capacity of 15 m3. These bulbs, such as lily bulbs, are cleaned using a sort of washing machine treatment. However, the sand present in water damages the bulb by etching into it. Moreover, this method produces large quantities of waste water for which there is no further use. Discharge is becoming increasingly less acceptable under current conditions.
By now feeding the bulbs, which, including the earth adhering thereto, have a specific mass that approaches the specific mass of water, through a bath in which rising air is moving, any soil material adhering to the bulbs is detached in a very gentle manner and brought into suspension and sludge material of this type precipitates by means of the mechanism described above.
It is possible to subject the sludge-enriched fluid to a further corresponding treatment, that is to say to pass it again through a bath with an air stream, as a result of which further concentration of the material can take place.
The invention also relates to a device for separating sludge-like material and water, comprising a container to be filled with water, which container is provided with feed means for said sludge-containing material.
According to the invention, the base of the container is provided with feed means for air, comprising perforated air feed elements, and a discharge for sludge arranged above these.
The device will be of different construction depending on the application of the method described above. When cleaning bulbs or other products, such products will be fed with the aid of a conveyor belt into a container which contains water or another suitable fluid. Air is passed through the container and the resulting deposit is discharged. The products are then removed from the container, likewise by mechanical means.
If, for example, manure has to be concentrated, it is not necessary to remove products from the container. After all, in this case there are, in principle, two waste streams, one containing concentrated sludge and the other containing treated fluid, such as water. However, it is possible to carry out a number of treatment steps and this is important especially in the case of the concentration of sludge-like materials. According to the invention, an assembly comprising a number of devices located downstream of one another in the direction of flow is proposed for this purpose.
Essentially the same quantity of water can still be used with the method now proposed. The quantity of moisture in the discharge sludge is relatively small. Consequently, small quantities of waste water are produced, which appreciably reduces the problems associated with cleaning. Pre-treatment and after-treatment devices can be located upstream and downstream of the device according to the invention. An example of a pre-treatment device which may be mentioned is a vacuum chamber with which adhering porous parts are detached. An after-treatment device can be a separator device in order to enable the used rinsing water to be recycled. An (infra red) drying device for the crop can also be provided.